Various circuit arrangements for triggering a load which is connected in the shunt arm of a bridge circuit are known from power electronics. In vehicle engineering, such circuits are used for auxiliary drives e.g. for electric window winders, sunroof adjustments, seat adjustments and actuators for headlamp cleaning systems. In modern motor vehicles these circuits are expected to include self-diagnosis functionality. Before the circuit is activated, such a self-test should detect whether there is a short circuit from load leads to ground or supply voltage, or a break in the connection cables (open-load detection).
The circuit-based implementation of the self-diagnosis functionality can be designed such that, for example, the current or the voltage in the shunt arm of the H circuit is measured and this status information is supplied to the control circuit. A further possible solution could consist in using semiconductor switches which are capable of self-diagnosis in the bridge circuit, whose status information is again supplied to the control circuit and is analyzed by a test program which is stored there.
Both solution options have the disadvantage that each feedback of status information occupies a signal connection in each case. This involves corresponding cost overheads in relation to the control circuit. If the control circuit consists of a microcontroller, a specific type is predetermined by the number of I/O pins which are occupied for testing purposes. This type also implies a specific size, which is disadvantageous in particular if the electronic components of the control circuit and the switch elements of the bridge circuit and the actuator must be miniaturized.